PROJECT SUMMARY The design of public insurance in providing mental health services is a critically important policy issue. A large number of studies have demonstrated substantial benefits for patients in integrated care models, which allow access to primary physical and mental health care in one setting. However, widespread adoption of integrated care models has not occurred. A critical and continuing barrier is the separation of financing and payment for physical and mental health services, particularly in the form of mental health ?carve-outs? in Medicaid programs. Carve-outs are perceived to create barriers and hamper the aspirational potential of integrated care. To understand the potential for states to widely disseminate integrated care, we propose to study Washington State?s ?Integrated Managed Care? (IMC) initiative. Under this initiative, Medicaid beneficiaries will receive comprehensive physical and mental health services through a single, integrated managed care plan. The implementation of IMC takes place in a staggered fashion over the 2016-2020 timespan, with counties assigned to one of five waves that must transition from the existing carve-out system to IMC. This natural experiment creates an opportunity for a robust quantitative and qualitative study of the effects of full (financial and service) integration of physical and mental health. Our proposal leverages Washington?s Integrated Client Database System, a unique resource linking Medicaid claims to rich measures of social determinants of health, including housing, employment, and contacts with the criminal justice system. The proposed research seeks to enhance our understanding of how states can advance the use of integrated care, including the factors that may facilitate or hinder integration, and whether full financial integration can affect resource use or impact social determinants of health. We seek to fill these gaps in knowledge with the hope of providing actionable information to Medicaid agencies and health systems across the U.S., addressing questions about the feasibility and benefits of financial integration, with specific information about carving in or carving out services, the factors that facilitate integration at the clinical level, and the ways in which social service needs among individuals with severe mental illness are affected. This work is closely aligned with NIMH?s Strategic Objective 4.1 to ?improve the efficiency and effectiveness of existing mental health services,? which includes research to ?optimize financing models for adults and children with serious mental illnesses to provide efficient and effective care in public and private health care systems.? The combination of a strong natural experiment, detailed contextual data, and a rich set of outcomes will allow us to develop rigorous and actionable evidence to guide the provision of mental health services in Medicaid.